Blockade of ARHGAP11A reverses malignant progress via inactivating Rac1B in hepatocellular carcinoma

Specific effects of hypoxia-immune core gene ARHGAP11A on lung adenocarcinoma

Background

The changes in tumor microenvironment (TME) are closely related to the regulation of immunity and hypoxia. This study aimed to investigate the specific effects of ARHGAP11A on the prognosis, immunity, and hypoxia of lung adenocarcinoma (LUAD).

Methods

The core gene ARHGAP11A related to immunity and hypoxia was obtained from a variety of databases, including Gene Expression Omnibus (GEO), The Cancer Genome Atlas (TCGA), Human Protein Atlas (HPA), Tumor Immune Estimation Resource (TIMER), the Search Tool for the Retrieval of Interacting Genes (STRING), HALLMARK gene set, and various analysis methods (differences and single factor Cox analysis). The relationship between the expression level of ARHGAP11A, survival prognosis, immune invasion, and hypoxia regulation was analyzed.

Results

ARHGAP11A was associated with poor patient prognosis and was strongly associated with immune and hypoxic-related signal pathways. We also found that knocking down the expression of ARHGAP11A can affect the proliferation, glycolysis, migration, invasion, and anti-apoptotic ability of tumor cells. The changes of apoptosis-related proteins (BCL2, BAX, and Caspase-3), cell cycle protein E1, D1 (cyclin D1, cyclin E1), matrix metalloproteinase 2 and 9 (MMP2, MMP9), and P-Phosphatidylinositol 3-kinase and protein kinase B (P-PI3K and P-AKT) in the knockdown group, were verified by Western blot (WB). We also found that interfering with the expression of ARHGAP11A can reduce the expression of programmed cell death ligand 1 (PDL1) in LUAD cells. Through the induction of tumor cells by cobalt chloride (CoCL2), we established a hypoxic microenvironment, and found that interfering with ARHGAP11A can significantly reduce the expression of hypoxia-inducible factor 1A (HIF1A), downstream molecular vascular endothelial growth factor A (VEGFA), and lactate dehydrogenase A (LDHA).

Conclusions

The expression of ARHGAP11A is highly correlated with immunity, hypoxia, poor prognosis, and tumor cell development. Therefore, the study of ARHGAP11A can provide more ideas on comprehensive treatment and prognosis management of LUAD.

The hGIDGID4 E3 ubiquitin ligase complex targets ARHGAP11A to regulate cell migration

The human CTLH/GID (hGID) complex emerged as an important E3 ligase regulating multiple cellular processes, including cell cycle progression and metabolism. However, the range of biological functions controlled by hGID remains unexplored. Here, we used proximity-dependent biotinylation (BioID2) to identify proteins interacting with the hGID complex, among them, substrate candidates that bind GID4 in a pocket-dependent manner. Biochemical and cellular assays revealed that the hGIDGID4 E3 ligase binds and ubiquitinates ARHGAP11A, thereby targeting this RhoGAP for proteasomal degradation. Indeed, GID4 depletion or impeding the GID4 substrate binding pocket with the PFI-7 inhibitor stabilizes ARHGAP11A protein amounts, although it carries no functional N-terminal degron. Interestingly, GID4 inactivation impairs cell motility and directed cell movement by increasing ARHGAP11A levels at the cell periphery, where it inactivates RhoA. Together, we identified a wide range of hGIDGID4 E3 ligase substrates and uncovered a unique function of the hGIDGID4 E3 ligase regulating cell migration by targeting ARHGAP11A.

Identification of a central network hub of key prognostic genes based on correlation between transcriptomics and survival in patients with metastatic solid tumors

Background

Dysregulated pathways in cancer may be hub addicted. Identifying these dysregulated networks for targeting might lead to novel therapeutic options.

Objective

Considering the hypothesis that central hubs are associated with increased lethality, identifying key hub targets within central networks could lead to the development of novel drugs with improved efficacy in advanced metastatic solid tumors.

Design

Exploring transcriptomic data (22,000 gene products) from the WINTHER trial (N = 101 patients with various metastatic cancers), in which both tumor and normal organ-matched tissue were available.

Methods

A retrospective in silico analysis of all genes in the transcriptome was conducted to identify genes different in expression between tumor and normal tissues (paired t-test) and to determine their association with survival outcomes using survival analysis (Cox proportional hazard regression algorithm). Based on the biological relevance of the identified genes, hub targets of interest within central networks were then pinpointed. Patients were grouped based on the expression level of these genes (K-mean clustering), and the association of these groups with survival was examined (Cox proportional hazard regression algorithm, Forest plot, and Kaplan-Meier plot).

Results

We identified four key central hub genes-PLOD3, ARHGAP11A, RNF216, and CDCA8, for which high expression in tumor tissue compared to analogous normal tissue had the most significant correlation with worse outcomes. The correlation was independent of tumor or treatment type. The combination of the four genes showed the highest significance and correlation with the poorer outcome: overall survival (hazard ratio (95% confidence interval (CI)) = 10.5 (3.43-31.9) p = 9.12E-07 log-rank test in a Cox proportional hazard regression model). Findings were validated in independent cohorts.

Conclusion

The expression of PLOD3, ARHGAP11A, RNF216, and CDCA8 constitute, when combined, a prognostic tool, agnostic of tumor type and previous treatments. These genes represent potential targets for intercepting central hub networks in various cancers, offering avenues for novel therapeutic interventions.

Clinical significance of upregulated Rho GTPase activating protein 12 causing resistance to tyrosine kinase inhibitors in hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is a major health challenge with high incidence and poor survival rates in China. Systemic therapies, particularly tyrosine kinase inhibitors (TKIs), are the first-line treatment for advanced HCC, but resistance is common. The Rho GTPase family member Rho GTPase activating protein 12 (ARHGAP12), which regulates cell adhesion and invasion, is a potential therapeutic target for overcoming TKI resistance in HCC. However, no studies on the expression of ARHGAP12 in HCC and its role in resistance to TKIs have been reported.

AIM

To unveil the expression of ARHGAP12 in HCC, its role in TKI resistance and its potential associated pathways.

METHODS

This study used single-cell RNA sequencing (scRNA-seq) to evaluate ARHGAP12 mRNA levels and explored its mechanisms through enrichment analysis. CellChat was used to investigate focal adhesion (FA) pathway regulation. We integrated bulk RNA data (RNA-seq and microarray), immunohistochemistry and proteomics to analyze ARHGAP12 mRNA and protein levels, correlating with clinical outcomes. We assessed ARHGAP12 expression in TKI-resistant HCC, integrated conventional HCC to explore its mechanism, identified intersecting FA pathway genes with scRNA-seq data and evaluated its response to TKI and immunotherapy.

RESULTS

ARHGAP12 mRNA was found to be highly expressed in malignant hepatocytes and to regulate FA. In malignant hepatocytes in high-score FA groups, MDK-[integrin alpha 6 (ITGA6) + integrin β-1 (ITGB1)] showed specificity in ligand-receptor interactions. ARHGAP12 mRNA and protein were upregulated in bulk RNA, immunohistochemistry and proteomics, and higher expression was associated with a worse prognosis. ARHGAP12 was also found to be a TKI resistance gene that regulated the FA pathway. ITGB1 was identified as a crossover gene in the FA pathway in both scRNA-seq and bulk RNA. High expression of ARHGAP12 was associated with adverse reactions to sorafenib, cabozantinib and regorafenib, but not to immunotherapy.

CONCLUSION

ARHGAP12 expression is elevated in HCC and TKI-resistant HCC, and its regulatory role in FA may underlie the TKI-resistant phenotype.

A novel ARHGAP family gene signature for survival prediction in glioma patients

ARHGAP family genes are often used as glioma oncogenic factors, and their mechanism of action remains unexplained. Our research entailed a thorough examination of the immune microenvironment and enrichment pathways across various glioma subtypes. A distinctive 6-gene signature was developed employing the CGGA cohort, leading to insights into the disparities in clinical characteristics, mutation patterns, and immune cell infiltration among distinct risk categories. Additionally, a unique nomogram was established, grounded on ARHGAPs, with DCA curves illustrating the model's prospective clinical utility in guiding therapeutic strategies. Emphasizing the role of ARHGAP30, integral to our model, its impact on glioma severity and the credibility of our risk assessment model were substantiated through RT-qPCR, Western blot analysis, and cellular functional assays. We identified 6 ARHGAP family genes associated with glioma prognosis. Analysis using the Kaplan-Meier method indicated a correlation between elevated risk levels and adverse outcomes in glioma patients. The risk score, linked with tumour staging and IDH mutation status, emerged as an independent factor predicting prognosis. Patients in the high-risk category exhibited increased immune cell infiltration, enhanced tumour mutational burden, more pronounced expression of immune checkpoint genes, and a better response to ICB therapy. A nomogram, integrating the risk score with the pathological features of glioma patients, was developed. DCA analysis and cellular studies confirmed the model's potential to improve clinical treatment outcomes for patients. A novel ARHGAP family gene signature reveals the prognosis of glioma.

Integrated analysis identified the role of three family members of ARHGAP in pancreatic adenocarcinoma

The Rho GTPase activating protein family (ARHGAPs) is expressed in pancreatic adenocarcinoma (PAAD) but its function is unclear. The aim of this study was to explore the role and potential clinical value of ARHGAPs in PAAD. Using TCGA and GEO databases to analyze expression of ARHGAPs in PAAD and normal tissues. Survival curve was drawn by Kaplan-Meier. ARHGAPs were integrated analyzed by GEPIA2, TIMER, UCLCAN, cBioPortal and R language. Protein level and prognostic value were evaluated via IHC staining or survival analysis. We totally identify 18 differentially expressed (DE) ARHGAPs in PAAD. Among the 18 DE genes, 8 were positively correlated with tumor grade; abnorrmal expression of 5 was positively correlated with copy number variation; expression of 4 was positively correlated with promoter hypomethylation. Multivariate Cox regression identified ARHGAP5, ARHGAP11A, and ARHGAP12 as independent prognostic factors of PAAD. The function of ARHGAPs was mainly related to GTPase activity and signaling, axon guidance, proteoglycans in cancer and focal adhesion. Expression of 7 ARHGAPs was strongly correlated with immune infiltration. Immunohistochemistry showed increased protein levels of ARHGAP5, ARHGAP11A, and ARHGAP12 in PAAD tissues. Survival analysis confirmed a negative correlation between ARHGAP5, ARHGAP11A, and ARHGAP12 expression and patient prognosis. Multivariate Cox regression proved ARHGAP5, ARHGAP11A, and ARHGAP12 could serve as independent prognostic indicators for PAAD. Finally, this study verified ARHGAP5, ARHGAP11A, and ARHGAP12 as independent prognostic factors in PAAD, suggesting their significance for the diagnosis and treatment of PAAD.

Machine learning and multi-omics data reveal driver gene-based molecular subtypes in hepatocellular carcinoma for precision treatment

The heterogeneity of Hepatocellular Carcinoma (HCC) poses a barrier to effective treatment. Stratifying highly heterogeneous HCC into molecular subtypes with similar features is crucial for personalized anti-tumor therapies. Although driver genes play pivotal roles in cancer progression, their potential in HCC subtyping has been largely overlooked. This study aims to utilize driver genes to construct HCC subtype models and unravel their molecular mechanisms. Utilizing a novel computational framework, we expanded the initially identified 96 driver genes to 1192 based on mutational aspects and an additional 233 considering driver dysregulation. These genes were subsequently employed as stratification markers for further analyses. A novel multi-omics subtype classification algorithm was developed, leveraging mutation and expression data of the identified stratification genes. This algorithm successfully categorized HCC into two distinct subtypes, CLASS A and CLASS B, demonstrating significant differences in survival outcomes. Integrating multi-omics and single-cell data unveiled substantial distinctions between these subtypes regarding transcriptomics, mutations, copy number variations, and epigenomics. Moreover, our prognostic model exhibited excellent predictive performance in training and external validation cohorts. Finally, a 10-gene classification model for these subtypes identified TTK as a promising therapeutic target with robust classification capabilities. This comprehensive study provides a novel perspective on HCC stratification, offering crucial insights for a deeper understanding of its pathogenesis and the development of promising treatment strategies.

Genome-wide association study for wattles trait in the dairy goat breed

Dairy goats are significant livestock that provide high-quality milk sources in the world. The wattles trait is an evident phenotypic character on the neck of a dairy goat, which is considered to be under genetic control. We collected samples of 189 dairy goats, including 94 with wattles and 95 without wattles, from four different farms and multiple dairy goat breeds. The samples were genotyped with the GeneSeek Genomic Profiler Goat 70 K SNP chip. Genome-wide association studies (GWAS) in wattles have identified associations with single nucleotide polymorphisms (SNPs) at chromosome 10. In this area, an extremely strong association locus was assigned to FMN1 (Formin 1) belongs to the formin homology family and is associated with limb deformity, other candidate genes of interest confirmed for wattles were ARHGAP11A (Rho GTPase Activating Protein 11 A) and GJD2 (Gap Junction Protein Delta 2). Meanwhile, we found the presence or absence of wattles had no significant effect on milk yield. This research will provide genetic resources useful to explore genetic factors affecting the trait.

Protooncogenic Role of ARHGAP11A and ARHGAP11B in Invasive Ductal Carcinoma: Two Promising Breast Cancer Biomarkers

Invasive duct carcinoma (IDC) is one of the most common types of breast cancer (BC) in women worldwide, with a high risk of malignancy, metastasis, recurrence, and death. So far, molecular patterns among IDC cases have not been fully defined. However, extensive evidence has shown that dysregulated Rho family small GTPases (Rho GTPases) including Rho GTPase activating proteins (RhoGAPs) have important roles in the invasive features of IDCs. In the current study, we analyzed the expression levels of two RhoGAP genes, ARHGAP11A and ARHGAP11B, in The Cancer Genome Atlas (TCGA) breast cancer (BRCA) and also our 51 IDC tumors compared to their matched normal tissues using quantitative polymerase chain reaction (qPCR). Our TCGA data analysis revealed higher expression of ARHGAP11A and ARHGAP11B in various cancers comprising BCs. Also, we found correlations between these genes and other genes in TCGA-BRCA. Moreover, our methylation analysis showed that their promotor methylation had a negative correlation with their overexpression. QPCR revealed their significant upregulation in our tumor samples. Furthermore, we found that the expression level of ARHGAP11A was considerably lower in women who were breastfeeding. Moreover, it had overexpression in cases who had regular menstrual cycles and early age (younger than 14) at menarche. However, ARHGAP11B had a higher expression in HER2-positive tumors versus HER2-positive and ER-positive tumors. Our study found possible protooncogenic roles for these genes and their involvement in IDC pathogenesis and malignancy. Therefore, they can be considered novel prognostic and diagnostic biomarkers for IDC.

ArhGAP11A mediates amyloid-β generation and neuropathology in an Alzheimer's disease-like mouse model

Amyloid-β (Aβ) plays an important role in the neuropathology of Alzheimer's disease (AD), but some factors promoting Aβ generation and Aβ oligomer (Aβo) neurotoxicity remain unclear. We here find that the levels of ArhGAP11A, a Ras homology GTPase-activating protein, significantly increase in patients with AD and amyloid precursor protein (APP)/presenilin-1 (PS1) mice. Reducing the ArhGAP11A level in neurons not only inhibits Aβ generation by decreasing the expression of APP, PS1, and β-secretase (BACE1) through the RhoA/ROCK/Erk signaling pathway but also reduces Aβo neurotoxicity by decreasing the expressions of apoptosis-related p53 target genes. In APP/PS1 mice, specific reduction of the ArhGAP11A level in neurons significantly reduces Aβ production and plaque deposition and ameliorates neuronal damage, neuroinflammation, and cognitive deficits. Moreover, Aβos enhance ArhGAP11A expression in neurons by activating E2F1, which thus forms a deleterious cycle. Our results demonstrate that ArhGAP11A may be involved in AD pathogenesis and that decreasing ArhGAP11A expression may be a promising therapeutic strategy for AD treatment.

ARHGAP11A Is a Novel Prognostic and Predictive Biomarker Correlated with Immunosuppressive Microenvironment in Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is a highly immunogenic tumor and immune dysfunction is associated with ccRCC poor prognosis. The RhoGTPase-activating proteins (RhoGAPs) family was reported to affect ccRCC development, but its role in immunity and prognosis prediction for ccRCC remain unknown. In the current study, we found ARHGAP11A was the only independent risk factor among 33 RhoGAPs (hazard ratio [HR] 1.949, 95% confidence interval [CI] 1.364-2.785). High ARHGAP11A level was associated with shorter overall survival (OS, HR 2.040, 95% CI 1.646-3.417) and ARHGAP11A is a prognostic biomarker for ccRCC. ARHGAP11A knockdown suppressed renal cell carcinoma (RCC) cell proliferation, colony formation, and migration, suggesting the promoting role of ARHGAP11A on RCC development. Mechanistically, ARHGAP11A might contribute to the suppressive tumor immune microenvironment (TIME). High ARHGAP11A level was correlated with infiltration of immunosuppressive cells (including T helper 2 (Th2) cells, regulatory T (Treg) cells, myeloid derived suppressor cells (MDSC), and M2 macrophage cells), activation of immunosuppressive pathways (IL6-JAK-STAT3 signaling and IFNγ response), and expression of inhibitory immune checkpoints (ICs). ARHGAP11A could promote T cell exhaustion and induce immune escape. ccRCC patients with low ARHGAP11A level were more suitable for immune checkpoint inhibitors (ICIs) therapy, while those with high ARHGAP11A level might benefit from a combination of ARHGAP11A blockade and ICIs. In all, ARHGAP11A might serve as a novel prognostic marker, therapeutic target, and predictor in the clinical response to ICIs therapy for ccRCC.

Subcellular mRNA localization and local translation of Arhgap11a in radial glial progenitors regulates cortical development

mRNA localization and local translation enable exquisite spatial and temporal control of gene expression, particularly in polarized, elongated cells. These features are especially prominent in radial glial cells (RGCs), which are neural and glial precursors of the developing cerebral cortex and scaffolds for migrating neurons. Yet the mechanisms by which subcellular RGC compartments accomplish their diverse functions are poorly understood. Here, we demonstrate that mRNA localization and local translation of the RhoGAP ARHGAP11A in the basal endfeet of RGCs control their morphology and mediate neuronal positioning. Arhgap11a transcript and protein exhibit conserved localization to RGC basal structures in mice and humans, conferred by the 5' UTR. Proper RGC morphology relies upon active Arhgap11a mRNA transport and localization to the basal endfeet, where ARHGAP11A is locally synthesized. This translation is essential for positioning interneurons at the basement membrane. Thus, local translation spatially and acutely activates Rho signaling in RGCs to compartmentalize neural progenitor functions.

Influence of AFP on surgical outcomes in non-B non-C patients with curative resection for hepatocellular carcinoma

To study the clinical and prognostic features of non-B non-C alpha-fetoprotein (AFP)(-)-hepatocellular carcinoma (HCC) (NBNC-AFP(-)-HCC) and the relationship between the prognostic features of HCC and hepatitis B virus surface antigen (HBsAg) status and AFP. We enrolled 227 patients who underwent hepatic resection for HCC between January 1998 and December 2007 at Sun Yat-sen University Cancer Center, all of whom were diagnosed with HCC by pathology. All patients were stratified into one of four groups (B-AFP(+)-HCC, B-AFP(-)-HCC, NBNC-AFP(+)-HCC, and NBNC-AFP(-)-HCC) according to AFP levels and HBsAg status. The clinicopathologic and survival characteristics of NBNC-AFP(-)-HCC patients were compared with those of all other three groups. Out of the 105 NBNC-HCC patients, 43 patients (40.9%) had AFP-negative HCC. There were some differences in factors between the B-AFP(+) and NBNC-AFP(-) patients, such as age, body mass index (BMI), diabetes, and ALT (P < 0.05). On univariate analysis, tumour size, secondary tumour, and portal invasion were prognostic factors for overall survival (OS) and disease-free survival (DFS) (P < 0.05). Cox multivariate regression analysis suggested that tumour size and tumour number (P < 0.05) were independent predictors. In addition, compared with the B-AFP(+)-HCC, B-AFP(-)-HCC, and NBNC-AFP(+)-HCC groups, the NBNC-AFP(-)-HCC patients had the best DFS (P < 0.05). Compared with the B-AFP(+)-HCC and NBNC-AFP(+)-HCC groups, the NBNC-AFP(-)-HCC patients had better OS (P < 0.05), and survival rates were similar to those of B-AFP(-)-HCC patients. NBNC-AFP(-)-HCC patients had a relatively favourable prognosis. It can serve as a useful marker in predicting the risk of tumour recurrence in the early stages.

RHO GTPase family in hepatocellular carcinoma

RHO GTPases are a subfamily of the RAS superfamily of proteins, which are highly conserved in eukaryotic species and have important biological functions, including actin cytoskeleton reorganization, cell proliferation, cell polarity, and vesicular transport. Recent studies indicate that RHO GTPases participate in the proliferation, migration, invasion and metastasis of cancer, playing an essential role in the tumorigenesis and progression of hepatocellular carcinoma (HCC). This review first introduces the classification, structure, regulators and functions of RHO GTPases, then dissects its role in HCC, especially in migration and metastasis. Finally, we summarize inhibitors targeting RHO GTPases and highlight the issues that should be addressed to improve the potency of these inhibitors.

Identification of key genes associated with cancer stem cell characteristics in Wilms' tumor based on bioinformatics analysis

Background

Nephroblastoma, also known as Wilms' tumor (WT), remains one of the major causes of tumor-related deaths worldwide in children. Cancer stem cells (CSCs) are considered to be the main culprits in cancer resistance and disease recurrence, which are reported in multiple types of tumors. However, the research on CSCs in WT is limited. Therefore, our study aimed to identify the key genes related to CSCs in WT to provide new ideas for treating WT.

Methods

The RNA-seq and clinical data of WT samples were obtained from the University of California Santa Cruz (UCSC) Xena database, which included 120 WT and six para-cancerous tissues. The mRNA stemness index (mRNAsi) based on mRNA expression was calculated to evaluate tumor stem cell characteristics in WT patients. A Kaplan-Meier (KM) analysis was performed to explore the clinical characteristics of the mRNAsi in WT. A weighted gene co-expression network analysis (WGCNA) was used to identify the key modules and genes related to the mRNAsi. A Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis was performed to explore the signaling pathways based on the key genes. The expression levels of the key genes were validated by the Gene Expression Omnibus (GEO) database. Further, the important upstream genes were identified by DisNor and gene co-expression analyses.

Results

The mRNAsi was significantly upregulated in WT (P=7.2e-05) and showed an upward trend in line with the pathological stage. Patients with lower mRNAsi scores had better overall survival (OS) than those with higher mRNAsi scores (P=0.0087). Eleven genes were defined as the key genes associated with the mRNAsi based on our WGCNA analysis [cor.MM (correlation. Module membership) >0.8 and cor.GS (correlation. Gene significance) >0.45] and were closely related to cell proliferation-related signaling pathways (P<0.05). Moreover, using protein interaction analysis, we identified ATM and CDKN1A as the key upstream regulatory genes of the 11 key genes.

Conclusions

Our study showed that the mRNAsi score was a potential prognostic factors in WT and identified the upstream genes ATM and CDKN1A and 11 genes closely related to the mRNAsi, which may provide new insights for CSC-targeted therapy in WT and improve clinical outcomes for WT patients.

Suppressive Role of ACVR1/ALK2 in Basal and TGFβ1-Induced Cell Migration in Pancreatic Ductal Adenocarcinoma Cells and Identification of a Self-Perpetuating Autoregulatory Loop Involving the Small GTPase RAC1b

Pancreatic ductal adenocarcinoma (PDAC) cells are known for their high invasive/metastatic potential, which is regulated in part by the transforming growth factor β1 (TGFβ1). The involvement of at least two type I receptors, ALK5 and ALK2, that transmit downstream signals of the TGFβ via different Smad proteins, SMAD2/3 and SMAD1/5, respectively, poses the issue of their relative contribution in regulating cell motility. Real-time cell migration assays revealed that the selective inhibition of ALK2 by RNAi or dominant-negative interference with a kinase-dead mutant (ALK2-K233R) strongly enhanced the cells' migratory activity in the absence or presence of TGFβ1 stimulation. Ectopic ALK2-K233R expression was associated with an increase in the protein levels of RAC1 and its alternatively spliced isoform, RAC1b, both of which are implicated in driving cell migration and invasion. Conversely, the RNAi-mediated knockdown or CRISPR/Cas9-mediated knockout of RAC1b resulted in the upregulation of the expression of ALK2, but not that of the related BMP type I receptors, ALK3 or ALK6, and elevated the phosphorylation of SMAD1/5. PDAC is a heterogeneous disease encompassing tumors with different histomorphological subtypes, ranging from epithelial/classical to extremely mesenchymal. Upon treatment of various established and primary PDAC cell lines representing these subtypes with the ALK2 inhibitor, LDN-193189, well-differentiated, epithelial cell lines responded with a much stronger increase in the basal and TGFβ1-dependent migratory activity than poorly differentiated, mesenchymal ones. These data show that (i) ALK2 inhibits migration by suppressing RAC1/RAC1b proteins, (ii) ALK2 and RAC1b act together in a self-perpetuating the autoregulatory negative feedback loop to mutually control their expression, and (iii) the ALK2 antimigratory function appears to be particularly crucial in protecting epithelial subtype cells from becoming invasive, both spontaneously and in a TGFβ-rich tumor microenvironment.

MicroRNA-30c-2-3p represses malignant progression of gastric adenocarcinoma cells via targeting ARHGAP11A

MicroRNAs are crucial tumor regulators to tumor development and progression. MiR-30c-2-3p can suppress malignant progression of tumor cells, but no study has reported the modulatory process of miR-30c-2-3p in gastric adenocarcinoma (GA). We herein investigated role of miR-30c-2-3p in GA cells. Here, we evaluated gene level in cancer cells by qRT-PCR. CCK-8, colony formation, flow cytometry, and transwell assays revealed biological functions of miR-30c-2-3p and ARHGAP11A. Genes downstream of miR-30c-2-3p were acquired through bioinformatics analysis. Our results suggested a low level of miR-30c-2-3p in GA tissue and cells, while its high expression could repress the malignant progression and promote cell cycle arrest and apoptosis of GA cells. Besides, ARHGAP11A was downstream of miR-30c-2-3p, with up-regulated ARHGAP11A facilitating malignant progression and repressing cell cycle arrest and apoptosis of GA cells. In addition, changes in GA cell functions caused by high ARHGAP11A expression could be partially offset by enhancing miR-30c-2-3p. Thus, our observations indicated that miR-30c-2-3p was a tumor repressor that could inhibit GA progression via modulating ARHGAP11A.

Overexpressed or hyperactivated Rac1 as a target to treat hepatocellular carcinoma

Despite novel targeted and immunotherapies, the prognosis remains bleak for patients with hepatocellular carcinoma (HCC), especially for advanced and/or metastatic forms. The rapid emergence of drug resistance is a major obstacle in the success of chemo-, targeted-, immuno-therapies of HCC. Novel targets are needed. The prominent roles of the small GTPase Rac1 in the development and progression of HCC are discussed here, together with its multiple protein partners, and the targeting of Rac1 with RNA-based regulators and small molecules. We discuss the oncogenic functions of Rac1 in HCC, including the contribution of Rac1 mutants and isoform Rac1b. Rac1 is a ubiquitous target, but the protein is frequently overexpressed and hyperactivated in HCC. It contributes to the aggressivity of the disease, with key roles in cancer cell proliferation, tumor metastasis and resistance to treatment. Small molecule targeting Rac1, indirectly or directly, have shown anticancer effects in HCC experimental models. Rac1-binding agents such as EHT 1864 and analogues offer novel opportunities to combat HCC. We discuss the different modalities to repress Rac1 overactivation in HCC with small molecules and the combination with reference drugs to promote cancer cell death and to repress cell invasion. We highlight the necessity to combine Rac1-targeted approach with appropriate biomarkers to select Rac1 activated tumors. Our analysis underlines the prominent oncogenic functions of Rac1 in HCC and discuss the modalities to target this small GTPase. Rac1 shall be considered as a valid target to limit the acquired and intrinsic resistance of HCC tumors and their metastatic potential.

Prognostic Value of Cancer-Associated Fibroblast-Related Gene Signatures in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a global health challenge with an increasing incidence worldwide. Cancer-associated fibroblasts (CAFs) function critically in HCC initiation and development. However, the prognostic significance of CAF-related gene signatures in HCC remains unknown. Therefore, the specific functions of CAF-related genes in HCC were investigated to help develop potential therapeutic strategies. In this study, CAF-related genes were screened from three CAF-related gene sets. HCC data from the Gene Expression Omnibus (GEO) database was applied to verify the screened CAF-related genes. Cluster analysis was used to identify clusters based on the expression pattern of CAF-related genes and two identified clusters were found to have a significant difference in overall survival (OS) and progression free intervals (PFI). The prognosis of HCC patients was predicted using the prognostic risk score model developed based on HCC data from The Cancer Genome Atlas (TCGA) databases. High-risk group patients had a worse OS than those in low-risk group in TCGA. These results were validated in International Cancer Genome Consortium (ICGC) database. Moreover, combining the clinicopathological characteristics related to prognosis with the model, a nomogram was built for a more accurate prediction of OS of HCC patients. In addition, analyses of immune infiltration characteristics of tumor microenvironment (TME), chemosensitivity, and immunotherapy response were conducted to further evaluate the prognostic value of CAF-related genes. Patients with low-risk scores were found to have higher chemosensitivity to cisplatin, doxorubicin, and sorafenib. Individuals with high-risk scores were found with a higher expression of most immune checkpoints which indicated patients with high-risk scores may benefit more from treatment with immune checkpoint inhibitors. Furthermore, a correlation between immune infiltration characteristics of TME and patients with different risk levels was found. These findings provide a possibility for the further development of personalized treatments in HCC.

ARHGAP11A Is a Prognostic Biomarker and Correlated With Immune Infiltrates in Gastric Cancer

Background: ARHGAP11A, belongs to RhoGAPs family, is vital for cell motility. However, the role of ARHGAP11A in gastric cancer is obscure. Methods: The expression level of ARHGAP11A was analyzed by Oncomine database. The correlation of ARHGAP11A expression with immune infiltrates and associated gene markers was clarified by Tumor IMmune Estimation Resource and Gene Expression Profiling Interactive Analysis database. The correlation between ARHGAP11A expression and the patient prognosis was identified by Kaplan-Meier plotter and PrognoScan. Genetic changes of ARHGAP11A were analyzed by cBioPortal. The protein-protein interaction network and gene functional enrichment analysis were constructed and performed by GeneMANIA and Metascape. Results: We found that the expression levels of ARHGAP11A were elevated in various cancers including gastric cancer when compared with normal tissues. High expression of ARHGAP11A was significantly correlated with a better prognosis in gastric cancer. We revealed that the expression of ARHGAP11A was negatively associated with infiltration levels of CD8+ T cells, CD4+ T cells, macrophages and dendritic cells. In addition, ARHGAP11A expression was significantly correlated with gene markers of these immune cells. Lastly, gene functional enrichment analysis indicated that ARHGAP11A involved in regulating lymphocyte activation, cell division, cell killing, myeloid leukocyte differentiation and leukocyte apoptosis. Conclusion: Our findings demonstrated that ARHGAP11A was a valuable prognostic biomarker in gastric cancer. Further work is needed to validate its role and underlying mechanisms in regulating immune infiltrates.

Negative regulation of TGFβ-induced apoptosis by RAC1B enhances intestinal tumourigenesis

RAC1B is a tumour-related alternative splice isoform of the small GTPase RAC1, found overexpressed in a large number of tumour types. Building evidence suggests it promotes tumour progression but compelling in vivo evidence, demonstrating a role in driving tumour invasion, is currently lacking. In the present study, we have overexpressed RAC1B in a colorectal cancer mouse model with potential invasive properties. Interestingly, RAC1B overexpression did not trigger tumour invasion, rather it led to an acceleration of tumour initiation and reduced mouse survival. By modelling early stages of adenoma initiation we observed a reduced apoptotic rate in RAC1B overexpressing tumours, suggesting protection from apoptosis as a mediator of this phenotype. RAC1B overexpressing tumours displayed attenuated TGFβ signalling and functional analysis in ex vivo organoid cultures demonstrated that RAC1B negatively modulates TGFβ signalling and confers resistance to TGFβ-driven cell death. This work defines a novel mechanism by which early adenoma cells can overcome the cytostatic and cytotoxic effects of TGFβ signalling and characterises a new oncogenic function of RAC1B in vivo.

LINC01207 promotes the progression of non-small cell lung cancer via regulating ARHGAP11A by sponging miR-525-5p

BACKGROUND

The disorder of LINC01207 has a significant regulatory effect on cancers, nevertheless its role in non-small cell lung cancer (NSCLC) have not been illustrated. This study investigated the regulatory effect of LINC01207 on NSCLC and clarify its molecular mechanism.

METHODS

Bioinformatics analysis was used to find the target lncRNA, miRNA and mRNA. LncBase and TargetScan databases predicted the relationship between LINC01207, miR-525-5p and ARHGAP11A. Dual-luciferase reporter gene assay and RNA binding protein immunoprecipitation assay were used to verify the binding relationship between genes. Fluorescence in situ hybridization assay was used to localize the expression of LINC01207 in NSCLC tissue. qRT-PCR and Western blot assays were used to measure the expression of LINC01207, miR-525-5p and ARHGAP11A. CCK-8 assay, Transwell assay and flow cytometry assay were used to detect NSCLC cell abilities. Mouse xenograft models further determined the effect of LINC01207 on the growth of NSCLC in vivo.

RESULTS

LINC01207 was up-regulated in NSCLC tissue and cells, which was mainly localized in the cytoplasm. LINC01207 knockdown could inhibit the proliferation, migration and invasion of cancer cells and induce cell apoptosis. In addition, silencing LINC01207 could suppress tumor growth in vivo. LINC01207 could sponge and inhibit the expression of miR-525-5p in NSCLC cells, and inhibiting LINC01207 and miR-525-5p simultaneously could reverse the effect of miR-525-5p on the progression of NSCLC cells. Further study on downstream target genes showed that miR-525-5p could restrain the expression of ARHGAP11A, and then affect the progression of NSCLC. LINC01207 acting as a competing endogenous RNA (ceRNA) could regulate the expression of ARHGAP11A by competitively binding with miR-525-5p.

CONCLUSION

LINC01207 regulates the progression of NSCLC by regulating the miR-525-5p/ARHGAP11A axis as a ceRNA and plays a carcinogenic role. In conclusion, our study elucidates the mechanism of LINC01207 regulating the progression of NSCLC, and provides a new idea for the diagnosis and treatment of NSCLC guided by lncRNA.

ARHGAP10 inhibits the epithelial-mesenchymal transition of non-small cell lung cancer by inactivating PI3K/Akt/GSK3β signaling pathway

Background

Rho GTPase activating protein 10 (ARHGAP10) has been implicated as an essential element in multiple cellular process, including cell migration, adhesion and actin cytoskeleton dynamic reorganization. However, the correlation of ARHGAP10 expression with epithelial–mesenchymal transition (EMT) in lung cancer cells is unclear and remains to be elucidated. Herein, we investigated the relationship between the trait of ARHGAP10 and non-small cell lung cancer (NSCLC) pathological process.

Methods

Immunohistochemistry was conducted to evaluate the expression of ARHGAP10 in NSCLC tissues. CCK-8 assays, Transwell assays, scratch assays were applied to assess cell proliferation, invasion and migration. The expression levels of EMT biomarkers and active molecules involved in PI3K/Akt/GSK3β signaling pathway were examined through immunofluorescence and Western blot.

Results

ARHGAP10 was detected to be lower expression in NSCLC tissues compared with normal tissues from individuals. Moreover, overexpression of ARHGAP10 inhibited migratory and invasive potentials of A549 and NCI-H1299 cells. In addition, ARHGAP10 directly mediated the process of EMT via PI3K/Akt/GSK3β pathway. Meanwhile, activation of the signaling pathway of insulin-like growth factors-1 (IGF-1) reversed ARHGAP10 overexpression regulated EMT in NSCLC cells.

Conclusion

ARHGAP10 inhibits the epithelial–mesenchymal transition in NSCLC via PI3K/Akt/GSK3β signaling pathway, suggesting agonist of ARHGAP10 may be an optional remedy for NSCLC patients than traditional opioids.

Different signaling and functionality of Rac1 and Rac1b in the progression of lung adenocarcinoma

Rac1 is a ubiquitously expressed Rho GTPase and an important regulator of the actin cytoskeleton. Its splice variant Rac1b exhibits a 19-amino acid (aa) in-frame insertion and is predominantly active. Both proteins were described in tumorigenesis or metastasis. We investigated the contribution of Rac1 and Rac1b to tumor progression of human non-small-cell lung adenocarcinoma (NSCLA). Rac1 protein was present in 8/8 NSCLA cell lines analyzed, whereas Rac1b was expressed in only 6/8. In wound-healing assays, enhanced green fluorescence protein (EGFP)-Rac1 slightly decreased cell migration, whereas proliferation was increased in both, Rac1- and Rac1b-expressing cells. In the in vivo chorioallantoic invasion model, EGFP-Rac1-expressing cells formed more invasive tumors compared to EGFP-Rac1b. This increased invasiveness correlated with enhanced phosphorylation of p38α, AKT and glycogen synthase kinase 3β (GSK3β), and activation of serum response- and Smad-dependent gene promoters by Rac1. In contrast, Rac1b solely activated the mitogen-activated protein kinase (MAPK) JNK2, together with TCF/LEF1- and nuclear factor kappa B (NFκB)-responsive gene reporters. Rac1b, as Rac1, phosphorylated p38α, AKT and GSK3β. Knockdown of the splicing factor epithelial splicing regulatory protein 1 (ESRP1), which mediates out-splicing of exon 3b from Rac1 pre-messenger RNA, resulted in increased Rac1b messenger RNA (mRNA) and suppression of the epithelial-mesenchymal transition (EMT)-associated transcription factor ZEB1. Our data demonstrate different signaling and functional activities of Rac1 and Rac1b and an important role for Rac1 in lung cancer metastasis.

Expression and prognostic analysis of Rho GTPase-activating protein 11A in lung adenocarcinoma

Background

Rho GTPase-activating protein 11A (ARHGAP11A) is a member of the Rho GTPase-activating protein (RhoGAP) subfamily. However, its expression, prognostic significance and clinicopathologic factors correlation in lung adenocarcinoma is still unclear.

Methods

The original gene expression profile, survival data, and clinical information of patients with lung adenocarcinoma (LUAD) were downloaded from The Cancer Genome Atlas (TCGA) database. The expression difference of ARHGAP11A between LUAD tissues and adjacent normal tissues in the TCGA database was analyzed by using R software, and verified by the Oncomine database and immunohistochemical (IHC) assay of LUAD sections. Logistic regression was applied to analyze the relationship between the expression of ARHGAP11A and clinicopathological factors of LUAD. Kaplan-Meier (KM) survival curves and a Cox proportional-hazards model were selected to evaluate the prognostic significance of ARHGAP11A expression. Gene set enrichment analysis (GSEA) software was applied to screen the tumor signaling pathways associated with the low and high expression group of ARHGAP11A in LUAD.

Results

The TCGA database showed that the expression of ARHGAP11A was significantly higher in LUAD tissues than in normal tissues (P<0.001). The up-regulation of ARHGAP11A in LUAD was verified by the Oncomine database (P<0.001) and IHC assay (P<0.001). Logistic regression analysis revealed the high expression of ARHGAP11A to be closely related to age, sex, advanced pathological stage, advanced T stage, and lymph node metastasis. The KM plots based on the TCGA and KM plotter databases indicated that patients with LUAD highly expressing ARHGAP11A had a poorer overall survival (OS) than patients with low expression of ARHGAP11A. Multivariate Cox regression analysis showed that the high expression of ARHGAP11A could be an important independent predictor of a poor prognosis of LUAD [hazards ratio (HR) =1.385; P<0.001]. GSEA indicated that 10 signal pathways were significantly enriched in LUAD samples with the ARHGAP11A expression phenotype.

Conclusions

ARHGAP11A may play a carcinogenic role in the malignant progression of LUAD, and it can be considered as a new independent prognostic factor and potential therapeutic target for LUAD.

Statistical profiling reveals correlations between the cell response to and the primary structure of Rho-GAPs

Rho-GTPase-activating proteins (Rho-GAPs) are essential upstream regulators of the Rho family of GTPases. Currently, it remains unclear if the phenotypic change caused by perturbations to a Rho-GAP is predictable from its amino acid sequence. Here we analyze the relationship between the morphological response of cells to the silencing of Rho-GAPs and their primary structure. For all possible pairs of 57 different Rho-GAPs expressed in MCF10A epithelial cells, the similarity in the Rho-GAP silencing-induced morphological change was quantified and compared to the similarity in the primary structure of the corresponding pairs. We found a distinct correlation between the morphological and sequence similarities in a specific group of RhoA-targeting Rho-GAPs. Thus, the family-wide analysis revealed a common feature shared by the specific Rho-GAPs.

Identification of novel biomarkers involved in pulmonary arterial hypertension based on multiple-microarray analysis

Pulmonary arterial hypertension (PAH) is a life-threatening chronic cardiopulmonary disorder. However, studies providing PAH-related gene expression profiles are scarce. To identify hub genes involved in PAH, we investigate two microarray data sets from gene expression omnibus (GEO). A total of 150 differentially expressed genes (DEGs) were identified by limma package. Enriched Gene Ontology (GO) annotations and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of DEGs mostly included mitotic nuclear division, ATPase activity, and Herpes simplex virus one infection. Ten hub genes from three significant modules were ascertained by Cytoscape (CytoHubba). Gene set enrichment analysis (GSEA) plots showed that transcription elongation factor complex was the most significantly enriched gene set positively correlated with the PAH group. At the same time, solute proton symporter activity was the most significantly enriched gene set positively correlated with the control group. Correlation analysis between hub genes suggested that SMC4, TOP2A, SMC2, KIF11, KIF23, ANLN, ARHGAP11A, SMC3, SMC6 and RAD50 may involve in the pathogenesis of PAH. Then, the miRNA-target genes regulation network was performed to unveil the underlying complex association among them. Finally, RNA extracted from monocrotaline (MCT)-induced Rat-PAH model lung artery tissues were to conduct quantitative real-time PCR (qRT-PCR) to validate these hub genes. In conclusion, our study offers new evidence for the underlying molecular mechanisms of PAH as well as attractive targets for diagnosis and treatment of PAH.

Proteasomal degradation of polycomb-group protein CBX6 confers MMP-2 expression essential for mesothelioma invasion

The aggressive invasiveness of malignant mesothelioma limits cancer therapy, however, the molecular mechanisms underlying the invasiveness remain largely unknown. Here we found that the matrix metalloproteinase-2 (MMP-2) was required for the invasion of mesothelioma cells in the collagen matrix and the gene expression of MMP-2 was correlated with the invasive phenotype. The MMP-2 gene expression was regulated by DNA and histone methylation around the transcription start site, implicating the involvement of the polycomb repressive complex (PRC). Knockdown of PRC component chromobox 6 (CBX6) promoted MMP-2 expression and invasion of mesothelioma cells. Transcriptome analysis suggested that CBX6 regulates sets of genes involved in cancer cell migration and metastasis. In invasive but not non-invasive cells, CBX6 was constantly unstable owing to ubiquitination and protein degradation. In human tissues, CBX6 localized in the nuclei of normal mesothelium and benign mesothelioma, but the nuclear staining of CBX6 was lost in malignant mesothelioma. These results suggest involvement of proteasomal degradation of CBX6 in mesothelioma progression.

Comprehensive analysis of transcriptome data stemness indices identifies key genes for controlling cancer stem cell characteristics in gastric cancer

BACKGROUND

Cancer stem cells (CSCs) are the tumor cell of origin with self-renewing ability and multi-differentiation potency. CSCs can play vital roles in gastric cancer (GC) metastasis and relapse. However, the genes that regulate the stemness maintenance of CSCs in GC patients remain largely unknown. In the present study, we sought to determine the key genes associated with stemness in GC patients.

METHODS

mRNA expression-based stemness index (mRNA SI) was analyzed with regard to the differential expression levels between normal and GC tissues, as well as clinical features and survival outcomes. Weighted gene co-expression network analysis (WGCNA) was performed to identify modules of interest and key genes. The differences in mRNA expression of key genes between normal and GC tissues were calculated by "ggpubr" package in R. Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) analysis were carried out to annotate the function of key genes. Protein-protein interaction (PPI) and gene co-expression analyses were conducted using STRING and "corrplot" package in R, respectively.

RESULTS

mRNA SI score was markedly increased in GC tumor compared to normal tissues. High mRNA SI score was remarkably associated with more advanced tumor stage and higher pathologic grade, but longer survival times. Based on the results of WGCNA, 19 key genes (i.e., BUB1, BUB1B, KIF14, NCAPH, RACGAP1, KIF15, CENPF, TPX2, RAD54L, KIF18B, TTX, KIF4A, SGO2, PLK4, ARHGAP11A, XRCC2, C1orf112, NCAPG, ORC6) were identified. GO and KEGG functional analyses revealed that these 19 key genes were mainly related to cell proliferation. From PPI and gene co-expression analyses, these 19 key genes were discovered to be intensively associated with each other at both protein and transcription levels.

CONCLUSIONS

our study identified 19 key genes that play vital roles in the stemness maintenance of CSCs in GC patients. Targeting these key genes may help to control CSC characteristics in GC.

Joint analysis of lncRNA m6A methylome and lncRNA/mRNA expression profiles in gastric cancer

Background

N ⁶-methyladenosine (m⁶A) modification might be closely associated with the genesis and development of gastric cancer (GC). Currently, the evidence established by high-throughput assay for GC-related m⁶A patterns based on long non-coding RNAs (lncRNAs) remains limited. Here, a joint analysis of lncRNA m⁶A methylome and lncRNA/mRNA expression profiles in GC was performed to explore the regulatory roles of m⁶A modification in lncRNAs.

Methods

Three subjects with primary GC were enrolled in our study and paired sample was randomly selected from GC tissue and adjacent normal tissue for each case. Methylated RNA Immunoprecipitation NextGeneration Sequencing (MeRIP-Seq) and Microarray Gene Expression Profiling was subsequently performed. Then co-expression analysis and gene enrichment analysis were successively conducted.

Results

After data analysis, we identified 191 differentially m⁶A-methylated lncRNAs, 240 differentially expressed lncRNAs and 229 differentially expressed mRNAs in GC. Furthermore, four differentially m⁶A-methylated and expressed lncRNAs (dme-lncRNAs) were discovered including RASAL2-AS1, LINC00910, SNHG7 and LINC01105. Their potential target genes were explored by co-expression analysis. And gene enrichment analysis suggested that they might influence the cellular processes and biological behaviors involved in mitosis and cell cycle. The potential impacts of these targets on GC cells were further validated by CCLE database and literature review.

Conclusions

Four novel dme-lncRNAs were identified in GC, which might exert regulatory roles on GC cell proliferation. The present study would provide clues for the lncRNA m⁶A methylation-based research on GC epigenetic etiology and pathogenesis.

GPCRs, G Proteins, and Their Impact on β-cell Function

Glucose-induced (physiological) insulin secretion from the islet β-cell involves interplay between cationic (i.e., changes in intracellular calcium) and metabolic (i.e., generation of hydrophobic and hydrophilic second messengers) events. A large body of evidence affirms support for novel regulation, by G proteins, of specific intracellular signaling events, including actin cytoskeletal remodeling, transport of insulin-containing granules to the plasma membrane for fusion, and secretion of insulin into the circulation. This article highlights the following aspects of GPCR-G protein biology of the islet. First, it overviews our current understanding of the identity of a wide variety of G protein regulators and their modulatory roles in GPCR-G protein-effector coupling, which is requisite for optimal β-cell function under physiological conditions. Second, it describes evidence in support of novel, noncanonical, GPCR-independent mechanisms of activation of G proteins in the islet. Third, it highlights the evidence indicating that abnormalities in G protein function lead to islet β-cell dysregulation and demise under the duress of metabolic stress and diabetes. Fourth, it summarizes observations of potential beneficial effects of GPCR agonists in preventing/halting metabolic defects in the islet β-cell under various pathological conditions (e.g., metabolic stress and inflammation). Lastly, it identifies knowledge gaps and potential avenues for future research in this evolving field of translational islet biology. Published 2020. Compr Physiol 10:453-490, 2020.

RAC1B: A Rho GTPase with Versatile Functions in Malignant Transformation and Tumor Progression

RAC1B is an alternatively spliced isoform of the monomeric GTPase RAC1. It differs from RAC1 by a 19 amino acid in frame insertion, termed exon 3b, resulting in an accelerated GDP/GTP-exchange and an impaired GTP-hydrolysis. Although RAC1B has been ascribed several protumorigenic functions such as cell cycle progression and apoptosis resistance, its role in malignant transformation, and other functions driving tumor progression like epithelial-mesenchymal transition, migration/invasion and metastasis are less clear. Insertion of exon 3b endows RAC1B with specific biochemical properties that, when compared to RAC1, encompass both loss-of-functions and gain-of-functions with respect to the type of upstream activators, downstream targets, and binding partners. In its extreme, this may result in RAC1B and RAC1 acting in an antagonistic fashion in regulating a specific cellular response with RAC1B behaving as an endogenous inhibitor of RAC1. In this review, we strive to provide the reader with a comprehensive overview, rather than critical discussions, on various aspects of RAC1B biology in eukaryotic cells.